In recent years, network connection via optical fiber in general households, mobile phones, and the like has become widely used, so that an increase in the transmission capacity of an optical network is required. In a backbone network, the transmission capacity of a carrier wave is increasing to 40 Gbps/100 Gbps.
On the other hand, since a propagation time of light in an optical fiber varies depending on a wavelength of light, as a transmission distance gets longer, a wavelength dispersion in which a light pulse waveform becomes dull occurs. If pulse broadening due to the wavelength dispersion occurs in a WDM (Wavelength Division Multiplex) system and the like which realize an optical transmission with a large capacity and long distance, a reception level significantly deteriorates to exert a harmful influence on the system. Therefore, in order to suppress dispersion generated in an optical fiber transmission line, a dispersion compensation for making the wavelength dispersion equal zero (cancelling the wavelength dispersion) is performed.
As attributes related to the dispersion compensation, there are fiber length between stations, amount of dispersion, dispersion slope, and the like. When building an optical communication network, values of these attributes need to satisfy conditions corresponding to the network design for performing the dispersion compensation.
When laying or maintaining optical transmission apparatus in a field, multiple attribute values such as a length of fiber laid between stations, an amount of dispersion and a dispersion slope need to be arbitrarily measured and monitored. As a conventional measurement technique for an optical fiber transmission line, it is disclosed in Japanese Laid-open Patent Publication No. 05-22323 that a technique in which a signal is transmitted from a monitoring device, a delay time of the looped back signal is measured, and a length of the optical fiber is measured is proposed.
When measuring a length of optical fiber and an amount of dispersion, an Optical Time Domain Reflectometer (OTDR) is generally used.
FIG. 20 is a diagram illustrating a measurement system using the OTDR. The OTDR 100 is arranged at an end of an optical fiber F to be measured. The OTDR 100 transmits a test light pulse toward the optical fiber F, and measures a time, an intensity level, and the like of the returned light from the reflection end.
Since a measurement principle of OTDR is basically to use a reflection, in an optical fiber measurement using a conventional OTDR, when the optical fiber is laid over a long distance (for example, when exceeding 100 km) or a light loss through the optical fiber is large, there is a problem that a correct measurement is difficult because an intensity level of the reflected light from a far-away end is low.
In addition, in a measurement using the OTDR, the system needs to be stopped.
FIG. 21 is a diagram illustrating that a halt of system operation is required. Optical transmission apparatuses 101 to 104 are connected by optical fibers in a ring shape.
In such a system, when trying to measure the length of optical fiber F1 connecting the optical transmission apparatus 103 and the optical transmission apparatus 104 using the OTDR, for example, it is required that the OTDR 100 is mounted on the optical transmission apparatus 104 and a reflection end is generated by releasing the optical fiber F1 connected to the optical transmission apparatus 103 (by disconnecting an optical connector). In this way, when using an optical measurement apparatus such as OTDR, the system operation must be stopped, so that there is a problem that maintenance is inefficient.
Furthermore, since conventional optical fiber transmission line measurements are not automated, connection and setting of optical measurement apparatus such as OTDR are performed manually one by one at a point to be measured, so that there is a problem that the conventional measurements lack not only maintainability but also convenience.